Polymers and copolymers of, and surgical devices made from lactide and/or glycolide and/or related compounds are well-known. See, e.g., U.S. Pat. Nos. 2,668,162, 2,683,136, 2,703,316, 2,758,987, 3,225,766:, 3,268,486, 3,268,487, 3,297,033, 3,422,181, 3,442,871, 3,463,158, 3,468,853, 3,531,561, 3,565,869, 3,597,449, 3,620,218, 3,626,948, 3,636,956, 3,736,646, 3,739,773, 3,772,420, 3,733,919, 3,781,349, 3,784,585, 3,792,010, 3,797,499, 3,839,297, 3,846,382, 3,867,190, 3,987,937, 3,878,284, 3,896,802, 3,902,497, 3,937,223, 3,982,543, 4,033,938, 4,045,418, 4,057,537, 4,060,089, 4,137,921, 4,157,437, 4,243,775, 4,246,904, 4,273,920, 4,275,813, 4,279,249, 4,300,565, and 4,744,365, U.K. Pat. or Appln. Nos. 779,291, 1,332,505, 1,414,600 and 2,102,827, D. K. Gilding et al., "Biodegradable polymers for use in surgery-polyglycolic/poly (lactic acid) homo-and copolymers: 1, "Polymer, Volume 20, pages 1459-1464 (1979), and D. F. Williams (ed.) Biocompatibility of Clinical Implant Materials, Volume II, chapter 9: "Biodegradable Polymers" (1981). Surgical devices prepared from copolymers containing lactide or glycolide and trimethylene carbonate have been described.
U.S. Pat. No. 4,429,080 describes glycolide end blocks and glycolide trimethylene carbonate random copolymer middle blocks. The block copolymers described in the '080 patent contain no 1,4 dioxane-2-one.
As another example, U.S. Pat. No. 5,066,772 describes random copolymers of lactide and trimethylene carbonate and triblock copolymers having lactide end blocks and lactidetrimethylene carbonate random copolymer center blocks. The block copolymers of the '772 patent do not include a block which has predominantly glycolic acid ester linkages.
Block copolymers described in U.S. Pat. 5,145,945 do not include a block having random copolymers of trimethylene carbonate and dioxanone nor do they include a block which is predominantly glycolide. In addition, see U.S. Pat. Nos. 4,243,775; 4,300,565; 4,705,820; 4,891,263; 4,916,193; 4,902,203; 5,037,950, and 5,252,701.
U.S. Pat. No. 4,452,973 describes triblock copolymers having polyglycolic acid end blocks and polyalkylene oxide middle blocks. Polyalkylene oxide also serves as a polymerization initiator for the polyglycolic acid blocks. U.S. Pat. No. 5,076,807 describes the use of polyalkylene glycol initiators for producing copolymers of dioxanone, glycolide and lactide.
Triblock copolymers having polyalkylene oxide middle blocks, are described in U.S. Pat. Nos. 4,438,253, 4,526,938, 4,716,203, 4,745,160, 4,857,602, and 5,019,094.
As described above synthetic bioabsorbable sutures are known in the art. However, in the manufacture of sutures an important characteristic of a suture is the amount of effort typically required to straighten the suture upon its removal from the package in order to ready the suture for use. This effort appears to be related to the "strain energy" of the suture, i.e., the integration of the stress-strain curve for the suture measured in kilogram-mm, and is equivalent to the work expended in elongating the monofilament by a specified percentage of its original length. As the strain energy of a given size of suture decreases so, too, does the amount of effort required to straighten the suture prior to use. A decrease in strain energy also appears to relate to the perceived flexibility of the suture, another important characteristic.
Another desirable characteristic of a bioabsorbable suture is its ability to exhibit and maintain desired tensile properties for a predetermined time period.
Absorbable sutures are manufactured from natural or synthetic materials. Synthetic absorbable multifilament sutures such as Dexon, Vicryl, and Polysorb commercially available from Davis & Geck (Danbury, Conn.), Ethicon, Inc. (Sommerville, N.J.), and United States Surgical Corporation (Norwalk, Conn.), respectively, are known in the industry as short term absorbable sutures. The classification short term absorbable sutures generally refers to surgical sutures which retain about 20 percent of their original strength at three weeks after implantation.
Long term absorbable sutures are generally known to be sutures which retain about 20 percent of their original strength at six or more weeks after implantation. For example PDS II and Maxon, synthetic absorbable monofilament sutures, commercially available from Ethicon, Inc. (Sommerville, N.J.) and Davis & Geck (Danbury, Conn.), generally fit this absorption profile.
Some of the earliest absorbable sutures were made from non-synthetic collagenous material taken from sheep's intestines. Such non-synthetic bioabsorbable sutures are still in use today and are commonly referred to as "catgut" or "gut sutures". Such sutures generally absorb quicker than short term absorbable sutures; retaining about 20 percent of their original strength at only two weeks after implantation. However, gut sutures may be undesirably stiff before subsequent treatment which renders them flexible and pliable. Commercially available gut sutures are immersed in tubing fluids (liquids used to achieve or enhance flexibility and pliability as well as to preserve the gut sutures, without effecting the suture's strength or integrity.), sterilized, and supplied to surgeons in packages containing the tubing solution.
Therefore, it would be advantageous to provide a bioabsorbable synthetic monofilament surgical suture which exhibits and maintains tensile properties and handling characteristics comparable to gut sutures, while providing the desired tensile strength retention profile and eliminating the need for tubing fluids.